Our studies of the human erythrocyte membrane proteins will continue to emphasize investigation of the transmembrane proteins. The human erythrocyte has two groups of such proteins: (a) The sialoglycoproteins (SGP), and (b) Those glycoproteins which do not contain sialic acid. Protein 3, the major membrane protein of the red cell which contains about 10% carbohydrate but little sialic acid, is an example of the latter group. The oligosaccharide chains of these proteins terminate for the most part with a galactose residue. The changes in these proteins and their role in aging of the erythrocyte will be investigated. The organization of the transmembrane proteins will also be studied using freeze-fracture techniques (see Fisher, SCience, 190: 983 (1975) and Edwards, Mueller and Morrison, Science, 203: 1343 (1979), which allows for the physical separation of the two halves of the bilayer. The crosslinking of the transmembrane proteins by a variety of crosslinking reagents within the bilayer and in the hydrophobic portions of the protein out-side of the bilayer is under investigation.